2015ApJS..217....3M

We present an unprecedented spectroscopic survey of the Ca ii triplet + O i for a sample of 14 luminous (-26 ≳ M_V ≳ -29), intermediate redshift (0.85 ≲ z ≲ 1.65) quasars. The Infrared Spectrometer and Array Camera spectrometer on the ESO Very Large Telescope allowed us to cover the Ca ii near-infrared spectral region redshifted into the H and K windows. We describe in detail our data analysis which enabled us to detect Ca ii triplet emission in all 14 sources (with the possible exception of HE0048-2804) and to retrieve accurate line widths and fluxes of the triplet and O i λ8446. The new measurements show trends consistent with previous lower-z observations, indicating that Ca ii and optical Fe ii emission are probably closely related. The ratio between the Ca ii triplet and the optical Fe ii blend at λ4570 Å is apparently systematically larger in our intermediate redshift sample relative to a low-z control sample. Even if this result needs a larger sample for adequate interpretation, higher Ca ii/optical Fe ii should be associated with recent episodes of star formation in intermediate redshift quasars and, at least in part, explain the apparent correlation of Ca ii triplet equivalent width with z and L. The Ca ii triplet measures yield significant constraints on the emitting region density and ionization parameter, implying Ca ii triplet emission from log(n_H) ≳ 11 [/cm3]and ionization parameter log U ≲ -1.5. The line width and intensity ratios suggest properties consistent with emission from the outer part of a high-density broad line region (a line emitting accretion disk?).